Method of pressure treatment of metallic melts, especially steel melts



April 30, 1968 R. HENTRICH ET AL 3,380,509

METHOD OF PRESSURE TREATMENT OF METALLIC MELTS, ESPECIALLY STEEL MELTS Filed Aug. 16, 1965 5 Sheets-Sheet 1 F/ 1 PRIOR Mr INVENTORS PRI H sub-rel,

Aprll 30, 1968 R. HE RICH ET 3,380,509

METHOD PRESSU TR TMENT OF METALLIC M S, ESPECIAL STEEL MELTS Filed Aug. 16, 1965 5 Sheets-Sheet 2 FIG. 2

INVENT 5 ?ober$ an 114 Apnl 30, 1968 R. HENTRICH ET AL 3,380,509

METHOD OF PRESSURE TREATMENT OF METALLIC MELTS, ESPECIALLY STEEL MELTS Filed Aug. 16, 1965 E: Sheets-Sheet Z- Pa-Pl' 35 37 FIG. 3

30 Wanda 6f April 30, 1968 R. HENTRICH ET AL 3,380,509

METHOD OF PRESSURE TREATMENT OF METALLIC MELTS, ESPECIALLY STEEL MELTS Filed Aug. 16, 1965 5 Sheets-Sheet 1 11' um I mllpml FIG. 4.

April 30, 1968 R. HENTRICH ET AL 3,380,509

METHOD PRESSURE TREATME OF METALLIC M MELTS S ESPECIALLY ST 5 Sheets-Sheet 5 Filed Aug. 16, 1965 raj United States Patent 3,380,509 METHOD OF PRESSURE TREATMENT OF METALLIC MELTS, ESPECIALLY STEEL MELTS Robert Hentrich and Alfred Randak, Geisweid, Germany, assignors to Stahlwerke Sudwestfalen AG., Geisweid, Germany Filed Aug. 16, 1965, Ser. No. 546,107 Claims priority, application Germany, Aug. 17, 1964, St 22,553 8 Claims. (Cl. 164-62) ABSTRACT OF THE DISCLOSURE Method and apparatus for treating and casting molten metal in which molten metal is transferred from a treatment vessel to a supply vessel and then at least a part of the metal is returned to the treatment vessel and is then again returned to the supply vessel, and molten metal is transferred from the supply vessel to a mold vessel for solidification therein, the metal being subjected to a pressure greater than atmospheric during at least at a part of the time it is in the treatment vessel and in said mold vessel.

This invention relates to processes and apparatus for treating metal melts, in particular steel melts, under varying pressures.

An object of the present invention is a process and and apparatus for the treatment of molten metals, in particular steel melts, under varying pressures, wherein treatment in a vacuum is followed by treatment at high pressure. Such a process is of interest, for instance, for certain austenitic steels in the case of which the melts are first of all treated in a vacuum to reduce oxygen and hydrogen contents to the lowest possible values, and, by treatment under excess nitrogen pressure, the nitrogen content is then increased above the value usual with melting under atmospheric pressure. Such steels possess, inter alia, by virtue of the increased nitrogen content, a much higher yield point and good tenacity.

A process for making such steels consists in the use of a combined vacuum and pressure induction furnace. Such furnaces are known. Thus, for example, Fresher and Kubisch reported to the Eisenhiittentage Conference at Leoben in 1963 (Ber-gund Huttenmannische Monatshefte 108 (1963), pp. 369 (et seq.), on experiments to do with nitrogenating steels in a 25 kg. (55 lbs.) capacity induction furnace with a test pressure of 300 lbs. wt./in. abs; Schneck, Frohberg and Heinemaun reported in Archiv. f.d. Eisenhiittenwesen (No. 9, 1962, p. 593) on experiments for absorption of nitrogen into fluid ferrous alloys, for which an ll-lb. capacity, vacuumand pressure-induction furnace for working pressures up to 75 lb. wt./in. was available. Such induction furnaces have the disadvantage that they are small and hence do not allow of the treatment of large melt weights. Even the largest vacuum-induction furnaces at present in existence, of 16,500 lbs. gross weight, are much too uneconomical in operation to make economical manufacture possible, if developed to vacuumand pressure-induction furnaces.

It is, therefore, an object of the present invention to provide a method of and apparatus for treating metallic melts, especially steel melts, which will overcome the above-mentioned drawbacks.

It is another object of this invention to provide a method of and apparatus for treating metallic melts, especially steel melts, by means of which melts produced with access of air in open melting appliances such as electric arc furnaces, open-hearth furnaces, and oxygenblast vessels, may be subjected to a combined vacuum 3,380,509 Patented Apr. 30, 1968 ice and excess pressure treatment following completion of melting.

It is also an object of this invention to provide a method and apparatus as set forth in the preceding paragraphs, which will be economical and will permit the carrying out of the process in a short time and with any desired weights of melt.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIGURES 1 and 2 are sectional elevations of two apparatuses heretofore proposed, and known to experts, for vacuum-treatment of molten metals;

FIGURE 3 is a similar view of one apparatus according to the invention for vacuumand excess pressuretreatment of molten metals;

FIGURES 4, 5 and 6 are similar views of other apparatuses according to the present invention.

In general, the present invention concerns a process of treating molten material such as steel melts, according to which the molten material to be treated and contained in a supply vessel is conveyed into a treatment vessel lined with refractory material above said supply vessel, which includes the steps of creating a pressure drop between the interior of said supply vessel and the interior of said treatment vessel, successively transferring molten material from said supply vessel into said, treatment vessel, and returning treated portions of said molten material from said treatment vessel back to said supply vessel.

The method according to the present invention may be carried out by an apparatus which includes: a supply vessel to receive the melt, a treatment vessel arranged thereabove with a suction pipe dipping into the melt for treatment of portions of the melt, a high-pressure-tight vessel surrounding the supply vessel, a high-pressure-tight hood enclosing the treatment vessel at least partially and the suction pipe entirely and forming together with the high-pressure-tight vessel 2. high-pressure-tight chamber separated from the atmosphere, first high-pressure supply means for producing a pressure p, 15 1b. wt./in. absolute in the high-pressur'e-tight vessel, second high-pressure supply means for producing a pressure p, 15 lb. wt./ in. absolute in the interior of the treatment vessel so that p p,, means for varying the distance between the supply vessel and the treatment vessel enabling the transport to and from the supply vessel, and means permitting adjustment of the pressure difference p,,p, to any positive value not exceeding a few pounds per square inch.

Referring now to the drawings in detail, the vacuumtreatment plant represented in FIG. 1 consists of a treatment vessel 1 with a refractory brick lining 11, the vessel 1 dipping, through a suction pipe 2 provided at its underside into a supply vessel 3, such as a ladle filled with liquid steel 13, provided with a refractory brick lining 12. FIGURE 1 is representative of the prior art.

The treatment vessel 1 is connected with a vacuum pump 4 and can be ventilated by means of a flood-valve 5. Apparatuses of such a construction for the vacuum treatment of melts were proposed as far back as 1889 (see Journal of the Iron and Steel Institute 1/1889, pp. 109/ 110 and FIG. XIII). By producing a vacuum in the treatment vessel 1, a part 14 of the melt 13 is drawn upwards by pipette effects into the treatment vessel 1, there degassed by the vacuum effect and then returned to the supply vessel 3 by breaking the vacuum in the vessel 1. Periodic repetition of this operation should finally result in the entire content 13 of the supply vessel 3 being gradually degassed. This process has enjoyed considerable technical success in a modified form, known as the DH- process, in which the periodic raising of a partial quantity 14 is not effected by periodic evacuation and breaking of the vacuum, but rather by periodic variation in the distance between the treatment vessel 1 and the supply 3 vessel with simultaneous continuous evacuation of the treatment vessel 1, i.e. without periodic interruption of the vacuum (see German Federal Republic Patent 1,062,396; a process and apparatus for effecting bath movements in fluid metals). The supply vessels (steel ladles) 3 used in this process have capacities of 9 to 400 tons of liquid steel. The size of the partial quantities 14 raised into the treatment vessel 1 is limited, however, in this process by the geometry of the treatment vessel 1 and supply vessel 3, since the maximum delivery height 760 torr torr 14.7 1b. wt./in.

If, thus, the bath surface of the melt 13 in the supply vessel 3 is so far below the rim 15 of this supply vessel 3 that the maximum delivery height h extends only to the upper bottom edge 16 of the treatment vessel, substantially no part 14 of the melt gets into the treatment vessel 1 and treatment is, herefore, not possible. Care must, therefore, be taken that the supply vessel 3 is constantly well filled in order to insure that vacuum treatment according to this process can be carried out.

In order to be independent of this limitation, it has been proposed inter alia to increase the pressure P, above the bath level of the melt in the supply vessel periodically above the atmospheric pressure. For this purpose it is necessary to seal off the space above the bath level of the melt 13 and periodically subject this space to an excess pressure. A possible construction of such an apparatus is shown in FIG. 2. In this drawing the supply vessel 3 is in a pressure-tight submerged tank 6 with concreted or steel-plate-reinforced walls 17. The treatment vessel 1 is located on the upper edge of the tank 6 with a cover 7 secured in a pressure-tight manner with the underside of the vessel 1. The connection 18 between the cover 7 and the tank 6 is sealed in such a manner as to be proof against excess pressure. The periodic delivery upwards of portions 14 of the melt is effected by periodically producing, for example by means of a pressure pump 8, a pressure of P 760 torr in the tank 6, and permitting the pressure AP, in excess of the atmospheric pressure to escape again through the valve 9. Depending on the excess pressure AP applied, a portion 14 of any desired size of the melt 13 is moved into the treatment vessel 1. The upper limit of the delivery pressure P to be applied depends on the geometry of the apparatus. In any case, it is of the order of a few pounds per square inch only. This can be illustrated by an example. The supply vessel 3 may be a steel ladle having a capacity of 660,000 lbs. Such a ladle has, for example, a mean cross-sectional area of 22,200 in. with a depth of the steel bath of 114 in. In order still to allow sufficient space for the inand out-flow of the melt, there must be a free space of at least 40 inches between the bottom 19 of the supply vessel 3 and the lower edge 20 of the suction pipe 2. The melt 13 can thus sink as low as the lower edge 20, i.e. by an amount of 80 inches. If it is assumed that the treatment vessel has a cross-sectional area only half as large as the ladle 3, lowering of the level of the melt 13 by 80 inches corresponds to an increase of the portion 14, of

the melt by 160 inches, that is, an increase in the difference 12' between the bath levels of Ah max.= in.+ in.=240 in.

This corresponds to an increase of the pressure p by This differential of 62.5 lbs. wt./in. represents the technically highest gauge pressure which can occur with such an apparatus. As, however, bath depths of 160 inches in the treatment vessel 1 prevent effective degassing reaction, bath depths of 540 inches are striven for. This, however, calls for the technically highest excess pressures P with such an apparatus being of the order of 30 lbs. wt./in. and at the same time the absolute pressure p above the melt 13 being of the order of 45 lbs. wt./in.

Apparatus as shown in FIG. 2 have not yet been industrially developed anywhere since it has hitherto always been possible so to adapt the geometry of apparatuses in accordance with FIG. 1 to the operating conditions, that no additional excess pressure AP was required in order to achieve an effective degassing. In all cases, therefore, it was preferred to use a periodical variation of the distance between the ladle 3 and the treatment vessel 1 rather than a periodic variation of the outside pressure 12 particularly since, in an apparatus according to FIG. 2 lifting gear for the treatment vessel was required in order to be able to start the process.

In the embodiment according to the present invention represented in FIG. 3, provision is made for the use of a much higher external pressure p than is permissible in apparatus according to FIG. 2. In order to compensate for the increased external pressure p the internal pressure p is also raised above the normal pressure, and employed for an excess pressure treatment of the melt. The periodic transfer of partial quantities 14 from the supply vessel 3 into the treatment vessel 1 is effected in this case by periodically varying the pressure difference p,,p As regards this difference, the same limitation applies, as was the case with the vacuum-treatment apparatus according to FIG. 2, with regard to pressure difference p,p, available for the transfer, this pressure difference being equal to-p as p -0 lb. wt./in. since this pressure difference must always be only of the order of magnitude of a few pounds .per square inch. In the case where a technically maximum available external pressure p =45 lb. wt./in. was given for the apparatus according to FIG. 2, a maximum available pressure difference p,,p -45 lb. wt./ in. corresponds in the case of pressure treatment. As, however, in the case of the vacuum-treatment apparatus according to FIG. 2, the pressure difference I -45 lb. wt./in. also corresponded to an absolute pressure p -45 lb. Wt./ir1. in the event of a pressure difference of, for example, p -p -45 lb. wt./in. with the combined vacuum and pressure treatment apparatus according to FIG. 3, any desired absolute pressure 2 is equal to or greater than p -p,-45 lb. wt./in. can be applied above the melt so long as an appropriate higher internal pressure p, in the treatment vessel 1 corresponds thereto.

The embodiment in accordance with FIG. 3 again incorporates all the component parts of the vacuum-treatment apparatus according to FIG. 1, that is, in particular a lined treatment vessel 1 with a suction pipe 2, a lined supply vessel 3, vacuum pump 4 and flood valve 5. The supply vessel is located in a pressure-tight tank 6 suitable for the maximum permissible working pressure p, which may be 1500 lb. wt./in. A hood 27 designed to withstand the same working pressure p,, can be held pressure-tight by' means of a packing 28 of usual kind over the tank 6. The entire treatment vessel 1 is mounted inside the hood 27 and for its part is constructed in a usual manner as a vacuum vessel whose containing walls must be suitable for a maximum operational pressure which corresponds to the maximum possible pressure difference p p,, thus,

for example, for p,,p' =45 lb. wt./in. This construction has the extraordinary technical advantage that the treatment vessel 1, lined with fast-abrading brickwork 11 and containing molten metal, does not require to with stand the whole treatment pressure p --p,, on its walls, but only the differential pressure p,,p which is appreciably less than the treatment pressure and, moreover, acts from the outside inwardly. If the treatment vessel should, in fact, burn through at any point, gas will enter from the outside through the leak with a pressure p, and cause an equalization of pressures whereupon the melt 14 runs back through the suction pipe 2 into the supply vessel 3. If, on the other hand, the hood 27 were not to enclose the treatment vessel, but be constructed similar to the hood 7 in FIG. 2, a leak in the region of the melt bath 14 would occasion projection of melt with great force into the open under the effect of the high internal presure p 15 lb. wt./in. and cause harm which can scarcely be contemplated. The external pressure p p moreover, would continuously feed fresh molten metal to the leak from the supply vessel 3.

The internal space 40 and external space 50 of the treatment vessel 1 are interconnected by a pipe 29 which contains a high-pressure pump 30 and a valve 31, further by a pressure-equalization valve 32 by which the internal pressure can be suited to the external pressure at any time, by a safety valve 33 which insures that the permissible pressure difference r -p, (e.g., 45 lb. wt./in. is never exceeded, and by safety valve 34 which always opens when the pressure in the internal space 40 exceeds the pressure in the external space 50. Pressure gauges 35, 36 and 37 indicate and control the external pressure p,,, internal pressure 2 and the differential pressure p,,p

The internal space, moreover, communicates through a conduit 39 with the vacuum pump 4. The vacuum conduit must be constructed, as far as a built-in valve 45, to withstand the maximum possible treatment pressure p, in the apparatus. This valve 45 must also withstand this pressure. The part of the conduit connecting between the valve 45 and the pump 4 need be constructed only as a simple vacuum conduit. A safety valve 25 opening when the pressure in the conduit rises above the surrounding pressure protects this part of the conduit and the whole pumping system from excessive pressures. A high-pressure pump 8 or a pressure-gas container 38 enables the external pressure p, in the space 50 to be raised to any required value within the permissible rated value. Owing to the action of the safety valve 33, the pressure p; inside the internal space 40 of the treatment vessel, is at the same time raised by an amount sufficient to prevent the permissible pressure difference p,,-p being exceeded. A pressure-equalization valve 9 enables the pressure p to be again equalized with the external atmospheric pressure at any time.

A combined vacuum and pressure treatment in an apparatus according to FIG. 3 may proceed as follows. The supply vessel 3 is set in the tank 6. Then the hood 27 together with the treatment vessel 1 and accessories is set down onto the sealing surface 28 so that the suction pipe 2 dips into the melt. While the vacuum-tight valves 5, 25, 31, 32, 33 and 34 remain closed, the main vacuum valve 45 is opened and the space 40 eXhausted by means of the pump 4. The melt 13 then rises in the suction pipe 2 by an amount conforming to the pressure difference p -p The pressure p in the outer chamber 50 is periodically raised by means of the pump 8 or the pressuregas container 38, and periodically lowered again through the equalization valve 9. In this way themelt 13 is raised in portions 14 periodically into the treatment vessel 1, is there degassed by the action of the sub-atmospheric pressure p, and flows back into the vacuum vessel 3. This periodic degassing is repeated until there is achieved a sufficiently marked reduction of the volatile elements, such as oxygen, carbon, hydrogen, nitrogen in the vacuum. In practice, this is achieved after the total weight of the melt has been transferred three times to and from the treatment vessel. If degassing is all that is required, the treatment is now finished. The pump 4 is switched off, the valve 45 closed, and the valves 9 and 32 opened to equalize the pressure with the atmosphere. If, however, following the degassing, it is desired to conduct a pressure treatment somewhat below 750 lb. wt./in. nitrogen pressure, it is necessary only to close the excess-pressuretight main vacuum valve 45 and stop the pump 4. Then, by means of the pump 8 or pressure-gas container 38, the pressure p in the space 50 is raised to e.g., 795 lb. wt./in. the gas admitted being nitrogen. The pressure equalization valve 32 is left open, so that the pressure p in the internal space of the treatment vessel also rises to about 795 lb. wt./in. The whole apparatus is now under a reaction pressure of 795 lb. wt./in. In order to set the melt in motion so that it is able to react with the nitrogen atmosphere in the treatment Vessel 1 in portions 14 of the least bath depth, the pressure-equalization valve 32 is closed and the valve 31 in the communicating pipe 29, is opened. By means of the small pump 30 now also under a pressure of 795 lb. wt./in. the internal pressure p, is now lowered from 795 to, say, 750 lb. Wt./in. absolute. This causes a portion 14 of the melt 13 to rise into the treatment vessel 1 offering a large reactive surface for reaction with the nitrogen. By closing the valve 31 and opening the valve 32, the pressures are again equalized and the portion 14 flows back into the supply vessel 3. By periodic repetition of the process, as many portions 14 are passed through the treatment vessel as are necessary to insure that the entire melt 13 has a sufliciently high nitrogen content. This completes the excess pressure treatment. To prevent the absorbed nitrogen from boiling off, the melt can then be teemed inside the closed pressure system. One way in which this can be done is shown in FIG. 3. Below the tapping hole 63, adapted to be opened by a compressed-air cylinder 61 and closed by a plug rod 62, there is a passage 64 into a second pressure chamber 60. A set of ingot molds 71, 72, is built into this chamber and these can be filled with the melt 13 through a funnel 65. On completion of casting, the pressure chamber 60 is separated pneumatically from the chamber 50 by means of a valve 66. The melt contained in the ingot molds 71, 72, can now be allowed to freeze under a maintained pressure of, say, 750 lb. wt./ in. abs., while in the remaining part of the apparatus the pressure is equalized with the atmosphere, and preparations are made to repeat the next treatment.

The illustrated special kind of apparatus according to FIG. 3 is naturally only one explanatory of the principle. Many modifications are conceivable, especially in regard to the manner of teeming.

A very refined construction is shown in FIG. 4. In this apparatus, the supply vessel 3 is set onto a transporting carriage 101 and propelled on a track 102 through a pressure-tight gate 103 into the interior of a stationary excesspressure chamber 150, which also contains the treatment vessel 1. The treatment vessel 1 is either lowered inside the pressure chamber, or, preferably, the supply vessel 3 is raised, as shown in FIG. 4 so that treatment can proceed as described with reference to FIG. 3. On completion of treatment, the vessel 3 is again lowered and run out on the truck 102 through a gate 104 in to a chamber 250 in which teeming is effected under pressure. For this purpose, the chamber 250 has an intermediate cover 105 on which ahe arranged a set of ingot molds 171, 172,

which can be filled through a riser pipe 106. The supply vessel 3 is again raised by means of a hoist until the pipe 106 is wholly immersed in the vessel 3. By lowering the pressure in the chamber 240 above the ingot molds 171, 172, by a few pounds per square inch (e.g. from 795 to 750 lb. wt./in. abs.) the melt rises in the molds which become filled. As soon as the supply vessel is empty, the riser pipe 106 is closed by means of a plug rod 107 and the supply vessel lowered. The supply vessel 3 is conveyed back into the chamber 160 by means of the carraige 101 and the gate 104 closed. Pressure equalization can be effected in the chamber 150, and the supply vessel 3 again taken into the open. After freezing of the melt in the ingot molds 171, 172, pressure equalization can also be effected in the chamber 250 and the ingots removed from the apparatus. For this purpose, the cover 105 together with the molds can be lowered onto the transporting carriage 102 and can be removed from the apparatus by means of this carriage.

It will be clear to those skilled in the art, that this construction of the apparatus is susceptible to changes of many kinds. Treatment and teeming, in particular, could take place in a common chamber. By making use of pressure-casting ingot molds made of graphite, pressure equalization with atmosphere could nevertheless be effected directly after casting is completed.

The apparatuses described with reference to FIGS. 3 and 4 may, of course, be furnished, as is the case with the so-called DH apparatus according to FIG. 1, with additional devices for heating the treatment vessel 1 and for addition of solid or fluid alloying constituents. The manner in which this can be achieved will be familiar to anyone skilled in the art.

FIG. 5 shows an apparatus with a modified form of treatment vessel. The treatment vessel 301 of this apparatus has at least two suction pipes 302 and 303 dipping into the melt. In this construction a pressure p is continuously maintained in an inner chamber 340, the pressure p being so far below the pressure p in the external chamber 350 that the pressure difference r -p can raise a portion 14 of the melt into the treatment vessel. By introducing a pump 304, such, for example, as a gas-lift pump or an electromagnetic pump, to or into at least one riser pipe 302, an upwardly directed flow is induced in the latter. Because of this the bath level in the chamber 340 rises and melt flows back into the supply vessel through at least one second pipe 303 as a result of the barometric sub-atmospheric pressure thereby occasioned. In this way there is no need for periodic variation of the pressure p in the inner chamber in order to introduce periodically fresh treatment material 14 into the treatment vessel. There is a constant flow of treatment material 14 up and down. In other respects the manner of operation is the same as in the embodiments according to FIGS. 3 and 4.

Finally, the embodiment according to FIG. 6 illustrates a modification of the invention wherein pressureand vacuum-treatment is combined with teeming on the continuous-casting principle. The apparatus comprises a common vessel 406, which inter alia may be subdivided into two chambers pneumatically separable from one another, and of which that shown is denoted 450 and that not shown serves for vacuumand pressure-treatment according to the invention. Teeming is effected in the chamber 450 in which there is at least one continuous-casting mold 471, an intermediate vessel 481 and a teeming mechanism for the supply vessel 403. In FIG. 6 the supply vessel 403 has a pouring spout and the teeming mechanism incorporates means (not shown) for tilting this vessel. The mold 471 is connected in a pressure-tight manner with the vessel 406, and so arranged that the gap 483 forming between the ingot 482 and the mold 471 acts as a dynamic seal (i.e., a specific quantity of gas flows continuously out through this gap 433).

Cooling means 490 or strand-drawing means, etc., may be provided externally of the pressure vessel 406 as in a normal continuous-casting apparatus. Cooling of the continuously-cast ingot 482 is so arranged that the wall thickness 488 between the unfrozen pool 434 and the external surface 485 at the exit of the ingot 482 from the vessel 406 is so great that it keeps out the excess pressure in the chamber 450. As an alternative solution a pressure-tight jacket 486 can be provided around the cooling means 490, and extend so far downwardly that the ingot 482, on

its emergence at 487 from the jacket 486, is frozen over its entire cross-section. The emergence point 487 must, therefore, again be formed as a dynamic seal.

All of the illustrated embodiments of the invention may be employed particularly advantageously when the fluid treatment material is stainless steel and moreover the gas used in the pressure treatment is nitrogen. The apparatuses according to FIGS. 1 to 6 have been especially designed with this manner of use in mind.

It is, of course, to be understood that the present invention is, by no means, limited to the particular methods and arrangements set forth above but also comprises any modifications within the scope of the appended claims.

We claim:

1. A method of treating molten material such as molten steel which comprises; supporting the molten material in a supply vessel, transferring molten material from the supply vessel to a treatment vessel above and in communication with the supply vessel, returning molten material from the treatment vessel to saigl supply vessel and maintaining inside the treatment vesselat least for part of the treatment time-21 pressure which is substantially higher than atmospheric pressure, delivering molten material from said supply vessel to a mold vessel for solidification therein, and maintaining a pressure greater than atmospheric in said treatment vessel during at least part of the time the molten material is therein and in said mold vessel during at least a part of the time the material is therein.

2. The method of treating molten material such as a steel melt which comprises; supporting the steel melt in a supply vessel arranged beneath a treatment vessel and which treatment vessel is in communication with said supply vessel, creating a pressure drop between the supply vessel and the treatment vessel whereby molten material is transferred from said supply vessel to said treatment vessel, returning treated molten material from the treatment vessel back to the supply vessel, and maintaining inside the treatment vesselat least for part of the treatment time-a pressure which is substantially higher than atmospheric pressure, delivering molten material from said supply vessel to a mold vessel for solidification therein, and maintaining a pressure greater than atmospheric in said treatment vessel during at least part of the time the molten material is therein and in said mold vessel during at least a part of the time the material is therein.

3. A method of treating molten material such as steel melts under pressures substantially greater than atmospheric pressure which comprises; arranging a supply vessel beneath a treatment vessel, communicating the treatment vessel with the supply vessel, creating a pressure in the supply vessel sufficiently greater than the pressure in the treatment vessel that molten material will be transferred from the supply vessel to said treatment vessel for treatment therein, returning treated molten material from said treatment vessel to said supply vessel, delivering molten material from said supply vessel to a mold vessel for solidification therein, and maintaining a pressure greater than atmospheric in said treatment vessel during at least part of the time the molten material is therein and in said mold vessel during at least a part of the time the material is therein.

4. The method of treating molten material such as steel melts in a treatment vessel positioned above a supply vessel and communicating therewith which comprises; placing the molten material in the supply vessel, enclosing said vessels in a gas tight enclosure with the supply vessel opening into said enclosure and with the treatment vessel sealed off from said enclosure, causing flow of molten material upwardly from the supply vessel into said treatment vessel and downwardly from said treatment vessel into said supply vessel, delivering molten material from said supply vessel to a mold vessel for solidification therein, and maintaining a pressure greater than atmospheric in said treatment vessel during at least part of the time the molten material is therein and in said mold vessel during at least a part of the time the material is therein.

5. The method of treating molten material such as steel melts in a treatment vessel positioned above a supply vessel and communicating therewith which comprises; placing the molten material in the supply vessel, enclosing said vessels in a gas tight enclosure with the supply vessel opening into said enclosure and with the treatment vessel sealed off from said enclosure, repetitively adjusting the pressure dilferential between the interior of said treatment vessel and the interior of said enclosure to such a degree as to cause molten material repetitively to flow from said supply vessel to said treatment vessel and then back into said supply vessel, delivering molten material from said supply vessel to a mold vessel for solidification therein, and maintaining a pressure greater than atmospheric in said treatment vessel during at least part of the time the molten material is therein and in said mold vessel during at least a part of the time the material is therein.

6. The method according to claim in which gas is exchanged between the interior of said treatment vessel and the interior of said enclosure to effect the said adjustment of the pressure difierential therebetween.

7. The method of processing molten metal which comprises; placing the molten metal in a supply vessel, placing the supply vessel beneath a closed treatment vessel and establishing communication between the vessels, establishing a pressure greater than atmospheric on the molten material in the supply vessel, varying said pressure repetitively to cause molten material to flow from the supply vessel to the treatment vessel and then back to the supply vessel a plurality of times until the entire body of molten material in the supply vessel is treated, disposing said supply vessel beneath an ingot mold and in communication therewith, establishing a pressure greater than atmospheric in the interior of the ingot mold and on the material in said supply vessel, establishing a pressure differential between the interior of the ingot mold and the material in said supply vessel to cause material to flow from the supply vessel into the ingot mold, and sealing oil the material in the ingot mold from return to the supply vessel for solidification of the material in the ingot mold while maintaining the pressure in the ingot mold above atmospheric.

8. The method according to claim 7 in which common enclosure means is provided for the supply vessel and the treatment vessel and for the supply vessel and the ingot mold, controlling the pressure within the enclosure means to control the pressure of the material in the supply vessel, and sealing otf at least the upper part of the ingot mold within the enclosure means to permit establishing of the said difierential pressure between the ingot mold and the supply vessel.

References Cited UNITED STATES PATENTS 493,047 3/1'893 Simpson 164-256 2,408,467 10/1946 Lyons 16466 2,893,860 7/1959 Lorenz 164-61 X 2,990,592 7/1961 Hursen 164-337 X 2,997,756 8/1961 Strom 164-62 3,022,059 2/1962 Harders 164-256 X 2,997,384 8/1961 Feichtinger 164-66 X 3,125,440 3/1964 Hornak 164-66 X 3,179,512 4/1965 Olsson 266-34 X 3,212,767 10/1965 Muller -93 FOREIGN PATENTS 623,922 2/ 1963 Belgium.

I. SPENCER OVERHOLSER, Primary Examiner.

WILLIAM J. STEPHENSON, Examiner.

R. S. ANNEAR, Assistant Examiner, 

